When you update or restore in iTunes, it reinstalls iOS. When you jailbreak, iOS is modyfied. So if you jailbreak, modifying iOS, and then you reinstall iOS, you lose your jailbreak. It's like when you reinstall Windows, you lose all of your installed programs.

Ok I replied again and this is what I said:
Follow these steps:
1. Open TinyUmbrella
2. Click "Start TSS Server"
3. Open iTunes but leave TinyUmbrella running
4. Hold the SHIFT key and click "Restore"
5. Select the 5.0.1 IPSW on your desktop
When it is finished, you will be on iOS 5.0.1 stock (not jailbroken).
If you want to jailbreak, then just click Jailbreak in redsn0w 0.9.10b6.